1. Field of the Invention
This invention relates to a radiation image read-out apparatus for reading out a radiation image from a stimulable phosphor sheet, on which the radiation image has been stored. This invention particularly relates to a radiation image read-out apparatus to be used in order to carry out an operation for reading out a radiation image, which has been stored on a stimulable phosphor sheet, from two surfaces of the stimulable phosphor sheet.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays, such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as the human body, is stored on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet is then scanned with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet when it is exposed to the stimulating rays is photoelectrically detected and converted into an electric image signal. The image signal is then processed and used during the reproduction of the radiation image of the object as a visible image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness. The ultimately obtained visible image may be reproduced as a hard copy or may be reproduced on a display device, such as a cathode ray tube (CRT) display device.
As a method for photoelectrically detecting light emitted by a stimulable phosphor sheet, a method has heretofore been known wherein a photoelectric read-out means for photoelectrically detecting the light emitted by the stimulable phosphor sheet is located only on the side of the stimulable phosphor sheet that is being scanned with the stimulating rays. The light emitted by one surface of the stimulable phosphor sheet is photoelectrically detected by the photoelectric read-out means. Also, a method for detecting light emitted by two surfaces of a stimulable phosphor sheet has been proposed in, for example, U.S. Pat. No. 4,346,295. With the proposed method for detecting light emitted by two surfaces of a stimulable phosphor sheet, two photoelectric read-out means are located on opposite sides of the stimulable phosphor sheet in order to photoelectrically detect the light emitted by the two surfaces of the stimulable phosphor sheet.
With the method for detecting light emitted by two surfaces of a stimulable phosphor sheet, a single radiation image is stored on the stimulable phosphor sheet, and the light emitted by two surfaces of the stimulable phosphor sheet is detected on the two sides of the stimulable phosphor sheet. Therefore, the efficiency, with which the light emitted by the stimulable phosphor sheet is guided and detected, can be kept high, and a high signal-to-noise (S/N) ratio can be obtained.
With the method for detecting light emitted by two surfaces of a stimulable phosphor sheet, which has been proposed in U.S. Pat. No. 4,346,295, the stimulable phosphor sheet is placed on a transparent holder, and two photoelectric read-out means (each of which comprises a combination of a light guide member and a photodetector) are respectively located above and below the holder. Specifically, the light emitted from the front surface of the stimulable phosphor sheet is detected by the photoelectric read-out means, which is located above the holder. Also, the light emitted from the back surface of the stimulable phosphor sheet is detected by the photoelectric read-out means, which is located below the holder.
However, with the aforesaid method for detecting light emitted by two surfaces of a stimulable phosphor sheet, the two photoelectric read-out means are respectively located on opposite sides of the stimulable phosphor sheet. Therefore, the apparatus for carrying out the method for detecting light emitted by two surfaces of a stimulable phosphor sheet cannot be kept small in size, and the cost of the apparatus cannot be kept low. Also, a large floor space is required to install the apparatus for carrying out the method for detecting light emitted by two surfaces of a stimulable phosphor sheet.